STUDY OF MINIMAL INHIBITORY CONCENTRATIONS AND MULTIPLE DRUG RESISTANCE PLASMIDS IN SALMONELLA TYPHI
1Pathologist, No. 7, AF Hospital, Kanpur 208 004.
Abstract:
S. typhi isolated from blood cultures were tested for minimal inhibitory concentrations of antimicrobial drugs using an simple easily fabricated multiple inoculator. Multiple drug resistant S. typhi were inhibited by high concentrations of ampicillin, sulphamethoxazole, trimethoprim and chloramphenicol (> 128 mg/L) suggestive of R factor mediated resistance. They showed presence of a single large plasmid with molecular weight ranging from 85 to 110 megadaltons. Sensitive S. typhi isolates were inhibited by lower concentrations of antimicrobial and did not show evidence of any plasmid. All isolates were equally sensitive to extremely low concentrations of ceftazidime, cefuroxime, ciprofloxacin, norfloxacin and gentamicin (< 0.5 mg/L).
Insights
Multiple drug-resistant Salmonella Typhi strains exhibit resistance to common antibiotics, linked to large plasmids. However, all strains remain sensitive to newer antibiotics like ciprofloxacin and gentamicin.
Area of Science:
- Microbiology
- Infectious Diseases
- Molecular Biology
Background:
- Salmonella Typhi (S. typhi) causes typhoid fever, a significant global health concern.
- Antimicrobial resistance in S. typhi poses a major challenge for effective treatment.
- Understanding the genetic basis of drug resistance, particularly plasmid-mediated resistance, is crucial.
Purpose of the Study:
- To determine the antimicrobial susceptibility patterns of S. typhi isolates from blood cultures.
- To investigate the presence and characteristics of plasmids in drug-resistant S. typhi.
- To evaluate the efficacy of various antibiotics against S. typhi, including newer agents.
Main Methods:
- Minimal inhibitory concentrations (MICs) of antimicrobial drugs were determined for S. typhi isolates.
- A simple, easily fabricated multiple inoculator was utilized for drug susceptibility testing.
- Plasmid DNA was extracted from resistant isolates and analyzed for molecular weight.
Main Results:
- Multiple drug-resistant S. typhi isolates showed high MICs for ampicillin, sulphamethoxazole, trimethoprim, and chloramphenicol.
- Resistant strains harbored a single large plasmid (85-110 megadaltons), suggesting R factor-mediated resistance.
- All S. typhi isolates, regardless of resistance profile, were highly sensitive to ceftazidime, cefuroxime, ciprofloxacin, norfloxacin, and gentamicin.
Conclusions:
- Plasmid-mediated resistance is a significant factor in the emergence of multidrug-resistant S. typhi.
- Emerging fluoroquinolones and cephalosporins, along with gentamicin, represent effective therapeutic options against S. typhi.
- Continued surveillance of antimicrobial resistance patterns in S. typhi is essential for public health.
